Coating of pre-cast electrophoresis slab gels

ABSTRACT

In pre-cast slab gel cassettes, the formation of pathways in which proteins can migrate between the gel and the walls of the cassette to form shadow bands is avoided by the application of a coating of a nonionic amphiphilic polymer to the cassette walls. The coating also prevents the gel from sticking to the walls when the gel is to be removed from the cassette after electrophoresis.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims the benefit of U.S.provisional patent application No. 60/241,381, filed Oct. 17, 2000, forall legal purposes capable of being served thereby. The contents ofprovisional patent application No. 60/241,381 are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to polyacrylamide gels as used in slab gelelectrophoresis.

Slab gels are particularly useful for electrophoresis in view of theirability to accommodate multiple sample analyses and the ease with whichthe electropherograms can be observed and read visually by identifyingthe locations of the various bands on the gels that correspond to theindividual components. Polyacrylamide is a gel material that is widelyused in slab gels.

Slab gels are frequently supplied in pre-cast form, retained between twoflat transparent plates in a cassette. The plates may be glass orplastic, a common plastic being a polystyrene-acrylonitrile blend. Adifficulty with certain pre-cast polyacrylamide gels is that they appearto separate from the cassette plates during storage, leaving a pathwaybetween the gel and one or both of the plates for the sample to migrate.This apparent pathway is detrimental to the electrophoretic analysissince the solute bands in the gel tend to migrate into the pathway andspread, forming shadow bands. A shadow band is a band of protein thatresults from the migration of protein away from a parent protein bandduring electrophoresis, the parent protein band being the well-definedband that is formed as a direct result of the electrophoreticseparation. Shadow bands reside mostly on the surface of the gel,whereas the parent protein bands extend relatively uniformly through thethickness of the gel. The pathways and shadow bands decrease the shelflife of precast gels and can eventually evolve into a smear of proteinon the surface of the gel. The shadow bands are a particular problem inpre-cast gels that have been stored without cooling.

Another problem encountered with polyacrylamide slab gels is a tendencyof the gels to stick or adhere to the plates. This presents a difficultyonce the separation has been performed and the user attempts to removethe gel from the plate for purposes of staining, photographing or otherobservation, detection or recordation. Attempts to remove a gel that issticking to one or both of the plates can result in a damaged gel and aruined experiment. This problem is especially acute for gels of lowconcentration and for gels used for isoelectric focusing.

The polymerization reaction to form polyacrylamide is inhibited whendissolved oxygen is present in the gel-forming liquid at or near the gelplate. This is especially true when the gel plates are plastic, such aspolystyrene-acrylonitrile, for example. To prevent this inhibition fromoccurring, a coating of polyvinylidene chloride or polyvinyl dichloride(PVDC) is often applied to the plates prior to contacting the plateswith the polyacrylamide gel material. Unfortunately, these coatingsproduce an effect on the electrophoresis image that appears to be theresult of separation between the gel and the plate. These coatings alsoexacerbate the sticking problem when the gel is an isoelectric focusinggel, for example one with a pH ranging from 5 to 8.

SUMMARY OF THE INVENTION

The present invention resides in the discovery that both the occurrenceof what appear to be pathways between a polyacrylamide gel and a gelcassette plate and the adherence of the gel to the plate can beprevented by applying a coating of a nonionic amphiphilic polymer to theplate surface before the gel is cast. The coating may be applieddirectly to the surface of the glass or plastic plate or it may beapplied over a polyvinylidene chloride or polyvinyl dichloride coatingif such a coating is present. Once the gels are formed over the coating,the gels can be stored for extended periods of time with no extraneouspath formation or sticking problem.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

Examples of nonionic amphiphilic polymers that can be used as coatingmaterials in the practice of this invention are polyvinyl alcohol,agarose, polyvinyl pyrrolidone, polyethylene glycol, polypropyleneglycol, polypropylene glycol/polyethylene glycol copolymers, and linearpolyacrylamide. Polyvinyl alcohol of 14,000 molecular weight(weight-average) for example can be applied as a 1% (by weight) aqueoussolution. For polyvinyl alcohol use in general, a weight-averagemolecular weight ranging from about 10,000 to about 100,000 may beapplied as an aqueous solution of concentration ranging from about 0.5%to saturation. For coatings of polyethylene glycol, an example is onewith a weight-average molecular weight of about 20,000, or a range offrom about 10,000 to about 100,000. The polyethylene glycol can beapplied as a 1-4% (by weight) aqueous solution. The concentrations andmolecular weights of other polymers are readily determined by routineexperimentation and will in many cases be readily apparent to thoseskilled in the art.

The nonionic amphiphilic polymer solution can be applied by any meansthat will result in a substantially even distribution over the platesurface and a clear film. Examples of application techniques are spincoating, dip coating, and brush coating. Once the film is applied, itcan be dried by conventional techniques before it is placed in contactwith the gel mixture. Drying can be accomplished by exposure to heat orto air. A particularly convenient drying method is to pass the coatedplate through an infrared tunnel.

The foregoing description is primarily for purposes of illustration.Further modifications, substitutions and variations will be apparent tothose skilled in the art and will be included within the scope of theinvention.

What is claimed is:
 1. A pre-cast polyacrylamide slab gel for use inslab gel electrophoresis, said pre-cast gel comprising: a pair ofchemically inert, transparent plates with inner surfaces coated withpolyethylene glycol; and a polyacrylamide gel cast between said plates.2. A pre-cast polyacrylamide slab gel for use in slab gelelectrophoresis, said pre-cast gel comprising: a pair of chemicallyinert, transparent plates with inner surfaces coated with a nonionicamphiphilic polymer; a coating of polyvinylidene chloride between eachplate and said coating of nonionic amphiphilic polymer; and apolyacrylamide gel cast between said plates.